Meeting breeding targets can be a challenge as you try to secure the right number of replacement gilts to breed at optimal maturity, which align with weaned sows. The good news is that there is a tool to help. PG600 is effective at stimulating large follicle development on the ovaries of non-cyclic females. It induces estrus and ovulation within a five-day period in a moderate to high percentage of treated females.

The name, PG600, comes from the two hormones — pregnant mares serum gonadotropin and human chorionic gonadotropin, at 400 and 200 units, respectively. It is labeled for use as a single 5-cc injection to stimulate estrus in prepubertal gilts of specific age and weight limits, and for use in anestrus sows. The dried powder is mixed with the diluent just before use and is injected in the neck muscle or subcutaneously. The decision to use PG600 is often based on a need to boost breeding consistency.

It can assist in developing replacement gilts and help reduce the number of gilts needed, which also alleviates pressures on housing space. For example, if you need five gilts to breed within a five-day window, you’d need a pool of 20 gilts. (That’s based on a 20-day estrus cycle and the fact that estrus onset is random.) If you needed 10 gilts in that window, the gilt pool would need to be 40 gilts. If the breeding window is shortened to three days, the pool would need to increase by 10 percent —  or four more gilts — for a total of 44.

In contrast, if you used PG600 in a pool of 20 prepubertal gilts you could expect 70 percent, or 14, of the gilts to be in estrus within three to five days, and at least 10 gilts would cycle in the same window 20 days later. That’s a 50 percent reduction in the replacement pool. By cutting that pool you reduce the gilt purchase or production costs; you also improve replacement-gilt feeding options, boar exposure and housing, which add to the herd’s reproductive performance and longevity.     

For PG600 to work best, gilts must be near their natural puberty age for the breed and farm, but cannot already be cycling. To find that window, select a pool of replacement gilts that are within five to 10 days in age. Expose them to a boar for 15 minutes a day using fence-line exposure or direct physical contact, starting at 150 days old and continuing until 220. Ideally, all gilts will cycle by the end of this period.

Deciding which gilts to treat and when will depend on the herd’s estrus pattern and which gilts have already been identified in estrus. You may decide to treat only gilts that did not cycle within a window between 160 and 220 days of age. As a last chance, you could treat any gilt that did not cycle by 220 days, and elect to keep it if it comes into heat. If it does not, you could sell the gilt without any lost market value or expense of non-productive days.

This has been shown effective for a high percentage of gilts that failed to naturally cycle after 25 days of boar exposure. Other ways to get more bang out of a shot of PG600 include making sure gilts weigh between 210 to 250 pounds (since heavier animals seem to respond better) and seeing that gilts are 160 to 200 days old.

You can further help synchronize a group by limiting boar exposure to the same time as the PG600 injection, or by regrouping and relocating gilts and then providing them with boar exposure.

Feeding is an overlooked factor that influences the PG600 response. See that the gilts’ lysine requirements are met and that weight gain continues. Do not limit-feed gilts until they have expressed estrus and have reached their optimal maturity to breed.

Choose the proper needle size and length for the injection. This will allow for quick injection and correct deposition. For producers who want to improve the PG600 response, subcutaneous injection may be advantageous, using a flank injection under the loose skin just off the animal’s leg. 

Historical assessment of the PG600 response in gilts shows a 70 percent estrus response in five days, with 80 percent ovulating, and an ovulation rate of 16 eggs.

Replacement-gilt management often suggests skipping an estrus before breeding. However, a producer’s need for breeding animals sometimes forces breeding at the first estrus, whether it’s natural or induced. If you must breed at the first PG600-induced estrus, see that the gilts are more than 180 days old and weigh more than 260 pounds.

Another issue to watch is the percentage of prepubertal gilts induced into estrus with PG600 that don’t continue to cycle 21 days later; it’s unclear why this occurs. So, before planning to skip a heat when using PG600, evaluate the immediate estrus response as well as 21 days later. It will provide an im-portant guideline for what to expect.

PG600 has been used to advance estrus in weaned sows and to prevent anestrus after weaning. The hormone is given to the sow in the farrowing stall at weaning. In a recent farm study, PG600 improved the number of sows mated within seven days of weaning, reduced the interval to estrus and improved the number of sows farrowing.

Data involving weaned sows show that PG600 consistently improves the number of sows mated and ovulating, and pigs produced by at least 10 percent compared to boar exposure alone. Infertility or delayed return to estrus is difficult to predict for sows, but in cases involving parity 1 and  2 sows, certain seasons (summer and fall) and situations of short lactation, PG600 often will stimulate ovarian activity.

Although PG600 can help reduce the severity of temporary infertility when circumstances are less than optimal, it is not a solution for poor management. Nor should it be a tool of last resort for infertile animals. It’s commonly used when breeding females have not been detected in estrus. However, PG600 will not induce estrus if the females are already cyclic, whether or not they have shown an estrus. Therefore, you must practice proper and approved estrus-detection procedures. 

PG600 will not cure pathologic abnormalities in cases with ovarian cysts, endometritis and pseudo-pregnancy. Infertility may relate to hormonal insufficiency in gilts or sows as a result of poor feed intake, a lowered metabolic state or reduced quality of the environment. PG600 can stimulate the ovaries and even induce estrus, but may not be able to completely override the other deficiencies. Recognizing the breeding herd’s infertility patterns will let you use PG600 in anticipation and prevention of fertility dips, letting you target the number of gilts and sows that you need to hit the breeding bull’s eye.


GETTING MORE SOWS TO FARROW

In a study on a commercial farm in Illinois, PG600 improved the number of sows bred within seven days of weaning by 12 percent. It also reduced the interval to estrus and increased the number of sows farrowing. 

Number females weaned:

No treatment   148      PG600   150

Number mated in 7 days:

No treatment   117      PG600   137

Percent mated within 7 days:

No treatment   79%      PG600   91%

Number of sows farrowing:

No treatment   107       PG600   128

Pigs born alive:

No treatment   10.7      PG600   10.5

Source: Rob Knox, University of Illinois


IDENTIFYING RESPONDERS

Here’s a look at the estrus status and response for gilts to be treated with PG600, with respect to age. It illustrates the expected proportions of non-responders, gilts already cycling and gilts that would respond to PG600.